Cellulosic product of improved strength and process therefor



United States Patent 3,269,852 CELLULOSIC PRODUCT 0F IMPROVED STRENGTHAND PROCESS THEREFOR Peter Jochen Borchert, Willard Lee Kaser, and JohnMirza, Elkhart, Ind., assignors to Miles Laboratories,

Inc., Elkhart, Ind., a corporation of Indiana No Drawing. Filed Feb. 1,1963, Ser. No. 255,700

4 Claims. (Cl. 106-213) This invention relates to the improvement of thephysical properties of cellulosic materials. In one of its moreparticular aspects this invention relates to a process for producingcellulosic materials of greatly enhanced strength characteristics,particularly high wet strength.

It has been known for some time that cellulosic fibers dispersed inwater have a negative surface potential and are therefore notsubstantive to various negatively charged materials whch could otherwisebe used to impart desired properties to the cellulosic fibers. Forexample, the polymeric aldehydes produced by the periodate oxidation ofpolysaccharides, referred to hereinafter as dialdehyde polysaccharides,are known to contribute strength characteristics to cellulosic fiberswhen utilized as additives to the wet end of the paper making process.However, the addition of dialdehyde polysaccharides to the negativelycharged cellulosic fibers has posed certain problems which it has beenpossible to solve only by resorting to involved and time consumingoperations in which the cellulosic fibers have been pretreated withchemical agents which reverse the charge of the cellulosic surface priorto the addition of a dialdehyde polysaccharide to the cellulosic fibers.

For instance, the aqueous fiber slurries have been contacted with suchstrongly cationic water-soluble materials as large amounts of alum,aqueous dispersions of cationic starches, polymeric amides and othersuitable cationic substances. This procedure is sometimes referred to asfiber pretreatment and the materials used for this purpose are known asretention aids or coupling agents. Once the cellulosic fibers have beenso treated, strongly anionic dispersions of dialdehyde polysaccharidesmay be added to the pretreated fibers and retained by means ofelectrostatic attraction. In recent years a variety of procedures havebeen developed in which dialdehy-de starch, a preferred dialdehydepolysaccharide, has been utilized as a wet end additive. Such proceduresare described in G. E. Hamerstrand, B. T. Hofreiter, C. L. Mehltretter,W. E. Schache and D. I. Kay, Tappi, 44, 430 (1961), and in B. T. Hofreiter, G. E. Hamerstrand, D. J. Kay and C. E. Rist, Tappi, 45, 177(1962).-

Most such processes utilize a dispersion of a dialdehyde polysaccharidein the presence of an inorganic bisulfite salt to render the dialdehydepolysaccharide strongly anionic.

Thus, in the prior art processes it is necessary to (1) add a suitableretention aid or coupling agent to the cellulosic fibers and (2)thereafter add to the pretreated cellulosic fibers a dispersion of astrongly anionic dialdehyde polysaccharide dispersion. In practice theprocess is carried out at various points in the manufacture ofcellulosic web materials. For instance, addition has been suggested atthe beater, t-he headbox, the fan pump, and various other points at thewet end of the manufacturing process.

Certain decided disadvantages to the aforementioned methods for thetreatment of cellulosic fibers have been encountered. One of thesedisadvantages is the uneconomical requirement for the use of relativelylarge amounts of retention aid or coupling agent. It is believed thatthe use of substantial proportions of such cationic materials results insurface areas of the fibers Patented August 30, 1966 ice which wouldotherwise be available as potential reaction sites for interactionbetween the cellulose and the aldehyde groups of the dialdehydepolysaccharide being occupied by these materials. This may be visualizedas a situation wherein the strength-imparting material has fewer contactpoints available at the fibers surfaces than are needed for fullstrength development.

Another disadvantage to the use of the aforementioned methods forimparting high wet strength to paper and other cellulosic materials liesin the problems inherent in the use of an inorganic bisulfite salt. Ithas been found that the use of bisulfite salts in the preparation ofdialdehyde polysaccharide dispersions limits the concentration of thesedispersions to a maximum of about 3%. The reason for this is that athigher concentrations highly viscous thixotropic gels are formed duringthe cooking procedures.- These gels have considerable resistance tobreak-down into fragments of lower molecular weight which break-down isnecessary for their successful use. Furthermore, no consistent heattransfer is possible after reaching the peak gel stage.

It is, accordingly, a principal object of this invention to providecellulosic materials which are characterized by having excellentstrength characteristics, particularly with respect to wet strength.

Another object of this invention is to provide a process for improvingthe properties of cellulosic fibers which is more economical and moreeffective than the aforementioned prior art processes.

A further object of this invention is to provide such a process which ischaracterized by practical convenience coupled with the attainment ofoptimum results.

Yet another object of this invention is to provide a process for thepreparation of cellulosic web materials which process may be readilyadapted to conventional techniques utilized in the manufacture of suchmaterials.

Other objects and advantages of this invention will be apparent to thoseskilled in the art from the following detailed disclosure anddescription.

It has now been found that the disadvantages inherent in previouslyavailable processes for the provision of cellulosic materials havingimproved strength characteristics can be overcome by means of a simpleand convenient technique for the treatment of cellulosic fibers. Theprocess generally comprises the cationization of a dialdehydepolysaccharide with a suitably formulated cationizing agent underconditions such that interaction be tween the cationizing agent and thedialdehyde polysaccharide results in the provision of a product which iscationic in nature and definitely substantive to anoinic cellulose. Thecationic nature of the reaction product between the dialdehydepolysaccharide and the cationizing agent can be demonstrated by means ofelectrophoresis. As developer certain anionic dyes such as Halopont BlueRN M (Du -Pont) can be used. This process results in full availabilityof the cellulosic fibers to adherence by a cationized dialdehydepolysaccharide. Other advantages, yet, .will accrue from the operationof this process; These additional advantages will be further disclosedbelow.

For the operation of the process of this invention a dialdehydepolysaccharide is first dispersed in water to form an aqueous dispersionof the dialdehyde polysaccharide. Dispersion is accomplished by heatinga dialdehyde polysaccharide in water to a temperature of about from 60C. to C. The concentration of the dialdehyde polysaccharide in theaqueous dispersion may be about from 1% to 30% by weight, preferablyabout from 3% to 10%. Cooking the rdialdehyde polysaccharide in waterfunctions to rupture the granules of the dialdehyde polysaccharide. Thecock is generally considered to be complete when no unruptured granulesare found to be phosphate, :borax or sodium hexametaphosphate.

'persion at the cooking temperature thereof.

present. This can be ascertained by means of centrifugation or by otherappropriate analytical means. Sometimes the dispersion of the dialdehydepolysaccharide can be facilitated by the use of a small amount of abuffer salt such as sodium acetate, sodium citrate, monosodium The useof such salts is particularly desirable where dispersions of relativelyhigh concentrations, for example, of above about 10% are required. Ingeneral, the amount of salt used should be in the range of about from0.1% to 5%, preferably about'from 0.5% to 2.5 of the weight ofdialdehyde polysaccharide used. Both the temperature of dispersion andthe necessity for use of a salt are to a large extent dependent upon thecomposition of the water used for preparing the dispersion. Forinstance,

water having a relatively high alkalinity, for example,

200 p.p.m. or higher, requires a cooking temperature, for a 3% to 5%dispersion, in the range of about from 60 C. to 70 C. Water of loweralkalinity, for example, about 100 p.p.m. or below, may require acooking temperature of upwards of about 80 C., for instance,temperatures in the range of about from 80 C. to 90 C. It should benoted that the use of low temperatures is possible where water of highalkalinity is used or where basic reacting buffer salts are added. Thetotal alkalinity may be defined as ten times the number of millilitersof 0.02 N sulfuric acid required to reduce the pH of a 100 milliliterwater sample to pH 4.0. This test is recorded as Tappi Standard T 62.0m55, Sheet 4.

Following the step of dispersing the dialdehyde polysaccharide .in waterthe pH of the resulting dispersion -is lowered to one in the range ofabout from pH 3.0

to pH 4.0 and preferably about pH 3.5. The lowering of the pH of thedialdehyde polysaccharide dispersion may be conveniently accomplished byadding any dilute acid such as hydrochloric acid, sulfuric acid orformic acid. Sulfuric acid is generally preferred for this purpose.

This pH adjustment prevents alkaline material which may be present inthe water used for preparing the dispersion from further degrading thedialdehyde polysaccharide. Such degradation results in undesirably lowwet strength being attained from use of such dispersions, especiallywhere the dispersions are subjected to long periods of heating. This pHadjustment also exerts beneficial effects in the later processing stepsserving to both catalyze the reaction between the dialdehydepolysaccharide and the cationizing agent and to prevent agglomerationupon interaction between these materials.

Following adjustment of the pH of the aqueous dialdehyde polysaccharidedispersion the cationizing agent to be used is added to the dialdehydepolysaccharide dis- The cationizing agent is then allowed to react withthe dialdehyde polysaccharide in dispersion for a period, generally, ofabout from one minute to minutes in length. The resulting dispersion ofcationized dialdehyde polysaccharide is of colloidal nature and may thenbe utilized in application to cellulosic fibers such as by adding saidcationized dialdehyde polysaccharide to an aqueous suspension ofcellulosic fibers such as found in the beater of a paper machine duringthe process of paper manufacture. Likewise, the addition may be atvarious other points in the paper making process or corresponding pointsin the processing of other cellulosic fibers. Wet strength increases inthe range of about 100 to 1000% over the blank have been realized usingthis process, depending on the type of fiber and the amount ofcationized dialdehyde polysaccharide added.

The suggested pH range of pH 3.0 to 4.0, and prefarably pH 3.5, is anoptimum one for facilitating the interaction between the disperseddialdehyde polysaccharide and the cationizing agent. Further, thecationized dialdehyde polysaccharide formed at this pH is a bydrophiliccolloid 'which has shown excellent stability upon prolonged storage withno formation of agglomerates. The use of ,these dispersions are used.

dispersions of dialdehyde polysaccharides which have not been pHadjusted as taught herein and having a pH above about pH 4.0, on theother hand, has resulted in the instantaneous agglomeration of colloidalparticles upon addition of the .cationizing agent. The use of suchdispersions results in very little, if any, wet strength improvement.

The amount of cationizing agent added to the dispersion of thedialdehyde polysaccharide depends upon its chemical nature. Economicconsiderations are also in volved. Optimum results vary with each typeused. The general range, however, is about from 1% to 50% by weight ofthe dialdehyde polysaccharide, and preferably about from 10% to 30%.

As pointed out above, the cationized dialdehyde polysaccharidedispersion may be incorporated into various points in celluloseprocessing. For example, in the paper making process it may beincorporated into the pulp slurry at any point at the wet end of thepaper machine. Alternatively, it may be applied from a tub size or at asize press or from showers to the dried or partially dried sheet.

The cationized dialdehyde polysaccharide dispersion prepared as abovedescribed has been found to be highly substantive to cellulosic fiberssuch that the addition of a salt such as aluminum sulfate is unnecessarywhere It is believed that the attractive forces between theelectropositively charged macromolecules of cationized dialdehydepolysaccharide and the electronegatively charged fiber surfaces are of asufficient magnitude to obviate the necessity for the use of any othersubstance.

The dialdehyde polysaccharides utilized in the process of this inventioncomprise a series of materials which are known to be capable ofcross-linking cellulose. These materials may be generally described aspolymeric dialdehydes, a preferred embodiment of which is dialdehydestarch. They are frequently referred to as periodate oxidizedpolysaccharides because of their preparation by the well known oxidationof polysaccharides with periodic acid. This preparation may beillustrated by the conversion of starch to dialdehyde starch orperiodate oxidized starch using periodic acid in accordance with thefollowing equation:

(l/H2011 H H C11 OH H HIO: i\| I L l l H OH 11 CHaOH C 0 II I] O O nwherein n stands for the number of repeating structural units in themolecule, which may range from as few as about 20 to as many as severalthousand. The preparation of dialdehyde starch is more particularlydescribed in US. Patent No. 2,713,553, to Charles L. Mehltretter.

The dialdehyde polysaccharide to be used in the process of thisinvention may be the dialdehyde derivative of any polysaccharide such ascorn, wheat, rice, tapioca or potato starches, amyloses, amylopectins,celluloses, gums, dextrans, .algins, inulins and others. Of thesepolysaccharides, the dialdehyde derivatives of starch known genericallyas dialdehyde starch are the best known and most widely used. However,where it is desired to have derivatives of other polysaccharides, thesemay be used as well.

In general, it is preferred to use dialdehyde polysaccharides which areabout from 90% to 100% oxidized, that is those wherein 90 to 100 of each100 of the original anhydroglucose units have been converted todialdehyde units such as by periodate oxidation as above described.

The cationizing agent may be characterized as a water solublenitrogen-containing polymer which is electropositively charged insolution. There are a wide variety of such materials which arecommercially available. For example, polyamides derived frompolyalkylene polyamines and dicarboxylic acids may be used. Aparticularly preferred group of such materials is described in US.Patent No. 2,926,154, to Gerald I. Keim. The polyamides described inthis patent are water soluble long chain polyamides containing therecurring groups:

wherein n and x are each 2 or more and R is :the divalent organicradical of a dicarboxylic acid. The incorporation of epichlorohydrininto the polyamide chain results in the formation of water solublecationic thermosetting resins. The amines which may be used in theformation of these polyamides include diethylenetriamine,triethylenetetramine, tetraethylenepentamine, dipropylenetriamine, andmixtures of polyethylene polyamines obtained by the reaction of ammoniawith ethylene dichloride. In addition, there may be included aliphaticdiamines such as ethylenediamine, propylenedi'amine,hexamethylenediamine and heterocyclic diamines such as piperazine or thelike. The dicarboxylic acids which may be used include the saturatedaliphatic dicarboxylic acids such as malonic, succinic, glutaric oradipic, and may also include diglyco-lic acid and blends of two or moreof these dicarboxylic acids. In addition, the higher saturated aliphaticdicarboxylic acids such as azelaic and sebacic acids may be included.

Another series of cationizing agents which have been found effective incarrying out the process of this invention are complex polymericWater-soluble materials which are multistage reaction products of anitrogenous compound such as dicyandiamide, acrylamide, urea, orguanidine and formaldehyde. A polycondensation product resulting fromthe reaction of dicyandiamide and formaldehyde has been found especiallyeffective. The degree of polymerization may be kept under strict controlso that a water-soluble condensate of low molecular weight forms. It isessential that no formation of insoluble matter is discernible in thewater-soluble condensate subsequent to its standing at room temperaturefor several years.

Such product is a colorless, viscous liquid with the mold-like odor offormaldehyde. The material is readily dilutable with water, cationicallyactive and chemically reactive. It imparts by itself no wet strengthproperties when added to aqueous fiber suspensions.

In addition to these specific exemplifications of cationizing agentswhich may be reacted with dialdehyde polysaccharides in accordance withthe process of this invention, it is possible to use a wide variety ofother materials as the cat-ionizing agent so long as these essentialrequirements are met:

The cationized dialdehyde polysaccharide dispersion may be added to anydesired cellulosic material. More particularly, these dispersions may beadded to a wide variety of cellulosic fibers or mixtures thereof. Forexample, any of the following as well as others may be successfullyemployed: unbleached kraft pulp, semi-bleached kraft pulp, bleachedkraft pulp, unbleached sulfite pulp,

. proximately 0.05%.

semi-bleached sulfite pulp, bleached sulfite pulp, unbleachedsemi-chemical pulp, semi-bleached semi-chemical pulp, bleachedsemi-chemical pulp, unbleached soda pulp, semi-bleached soda pulp,bleached soda pulp, unbleached and cooked cotton rag stock,semi-bleached and cooked cotton rag stock, bleached and cooked cottonrag stock, cooked bagasse fibers, either acid or alkali cooked cottonlinter pulp of various types and grades, mechanical pulp from bothconiferous and deciduous woods, cooked and semi-cooked hemp, sisal,ramie, jute, car-0a and other bast fibers such as bamboo, palm and manygrasses, old paper stock made up of any or all of any mixture of usedpapermaking fibers, cooked straw fibers, cooked flax fibers, and, infact, any fibrous cellulosic material that lends itself to the formationof water laid cellulosic webs or form fabrics from an aqueous suspensionof its fibers.

This invention will be better understood by reference to the followingdetailed examples which, however, are not to be considered as undulylimiting the scope of the in stant invention, which is defined in theclaims appended hereto.

EXAMPLE I Dispersion preparation A 5% dialdehyde polysaccharidedispersion using a water soluble cat-ionic thermosetting polyamide resinas cationizing agent was prepared as follows:

A quantity of 900 ml. of tap water was adjusted to a total alkalinity of100 p.p.m. (from 210 p.p.m.) using dilute sulfuric acid. The water washeated on a steam bath at C. and 50 g. of periodate oxidized corn starchwas added with stirring. The degree of oxidation of the periodateoxidized corn starch (dialdehyde starch) was 94% and the material had amoisture content of 9%. After 35 minutes of continued heating the slurryhad thickened and thinned out upon 10 more :minutes of heating. Then thepH of the dispersion was lowered to pH 3.5 using 5% sulfuric acid and 50ml. of Kymene 557, a water soluble cationic thermosetting polyamideresin available from Hercules Powder Company, was added. Kymene 557 issupplied as an aqueous solution containing 10% active ingredients. Theamount added corresponds to 10% on the weight of dialdehyde starch(solids basis). For complete interaction with the dialdehyde starchheating at 85 C. was continued for a period of 3 minutes. The reactionproduct was then cooled and the cationized dialdehyde starch dispersionwas ready for use.

SHEET-MAKING PROCEDURE The pulp was slurried in water to a consistencyof 1% and the pH of the slurry was adjusted to pH 4.5-5.5 with dilutesulfuric acid. The required amount of pulp slurry to make 20 sheets wasthen withdrawn and treated with the cationized dialdehyde starch. Aftermixing thoroughly 25.0 ml. portions of the treated slurry were measuredout for each 2.5 g. sheet and added to the prefilled Deckle box of aNoble and Wood sheet machine. Water used to fill the deckle box wasadjusted to a pH of 4.55.5. Pulp consistency in the deckle box was ap-After forming the sheet using a white water return system, the wet sheetwas pressed with a felt press of the Noble and Wood machine to aconsistency of approximately 32%. The sheet, still on the wire, was thendried at 220 F. during a three-minute drying cycle on the steam heateddryer of the sheet machine.

The blanks, in which no cationized dialdehyde starch was added wereformed in the same manner, omitting the addition of the cationizeddialdehyde starch.

TESTING OF HAND-SHEETS The hand-sheets were tested for dry tensilestrength and wet tensile strength using one-half inch strips over afour-inch span of the tensile tester. The wet and dry tensile data wereconverted to breaking length of paper ac- '7 cording to Tappi Standard T220, T 404. and T 456. The data are shown in Table I below:

'8 60 C. until all granules were disrupted and a uniform dispersionformed. This took a total of 30 minutes.

TABLE I Cationized Wet Breaking Dry Breaking dialdehyde Length, metersLength, meters Hand-Sheet Material starch added to oven dry (o.d.) pulp,Off Cured 1 Ofl Cured percent machine machine 1 a a: it? as; 0. 25 ,0 ggg lgleached Kraft 450 0.50 1,190 1, 470 8,907 9,000 1.00 1,700 2, 0008,810 8, 420 2. 50 2, 590 3, 470 9, 087 9, 860 0 1 8 as as; 0 25 961 7 9Northern Unbleached Kraft,

0. 50 1, 210 1, 330 9, 180 9, 270 450 1.00 1, 510 1, 780 9, 280 560 2.50 2, 540 2, 590 10, 400 10, 300 O I as 6 223 as 0.25 694 SouthernUnbleached Kraft 1 105 C. for 10 minutes.

EXAMPLE II Then 100 ml. of a 10% solution of Kymene 557 was A 5%dialdehyde starch dispersion using a water-Sol- 22222 325 g z gzg g i lf 3 3 uble dicyandiamide-formaldehyde polycondensation proddiluted to a801i g i fi f iig was e an not as cationizing agent was prepared in thesame manner Hand she t e f d d as described in Example I. Thedicyandiamide-formalscribed i is I Orme m 6 Same manner as dehyde pmductwas prepared as follows: The followin p results hown i T bl III b 1 To a50 gallon corrosion resistant kettle equipped with obtained withagbleachedsk ft C S F e OW were a recording thermometer, agitator,reflux condenser and m a jacket or coil for cooling were charged 154.6lb. of di- TABLE III cyandiamide, 248 1b. of 40% aqueous formaldehydeand Cationized dialdehyde Wet breakinglength 27.3 lb. Of ammoniumchloride. The slurry WEIS hea e Hand-Sheet Material starch added to o.d.(ofl machine), meters at 30 C., at which point an exotherm1c reactionstarted. P l Percent Within 30 to minutes the temperature rose to 70 C.and all sol-id material was in solution. After the exo- 3 2 fig thermicreaction came to a halt another 13.6 lb. of am- Bleached Kraft, 450 015021310 monium chloride was added. After 15 :minutes the last g3 37%;?part of the catalyst (13.6 lb.) was added and the mixture 40 was stirredfor three hours between 65 C. and 70 C. Then it was cooled. The totalsolids content was 67.5% (with catalyst), active ingredients 55.5%.Either 25 ml. or 50 ml. of a 30% solids containing solution of thisdicyand-iamide-formaldehyde-polycondensation product was added. Thiscorresponds to 15% and 30% additions of cationizing agent on the weightof dialdehyde polysaccharide. The sheet making procedure and testing ofthe hand-sheets were the same as shown in Example I.

In summary, this invention relates to cellulosic materials which haveenhanced wet and dry strength and to a convenient process for theirpreparation. The process comprises treating oellulosic fibers withareaction product of a dialdehyde polysaccharide and a cationizing agentwhich is:

1. Water soluble 2. Polymeric 3. Nitrogen-containing, and

The results obtained are shown 1n Table II below: 4. Cat1on1c 1n aqueoussolution.

TABLE II Cationized Wet breaking length, meters 1 Dry breaking length,meters 1 dialdehyde Hand-Sheet Material, starch added 450 cc. C.S.F. tooven dry Ofi machine Cured on machine Cured (o.d.) pulp, percent 0 211211 364 7, 363 7, 363 Northern bleached 0. 25 760 1, 290 1, 360 Kraft.0. 50 1, 330 1, 500 1, 610 1. 00 1, 753 1, 876 3, 080 2. 50 2, 880 3,127 3, 520 0 334 486 Northern Unbleached 0. 25 1, 220 1, 450 Kraft. 0.501, 570 1, 800 1. 00 2, 000 2, 600 2. 50 3, 010 3, 660

1 Percent dicyandiamide-formaldehyde polycondensation product solids onweight of dialdehyde starch.

EXAMPLE III What is claimed is:

1. A process for improving the physical properties of cellulosicmaterials which comprises reacting an aqueous dispersion of a dialdehydepolysaccharide containing from about 1 to about 30 weight percent of thedialdehyde polysaccharide with a water-soluble polymericnitrogen-containing cationizing agent selected from the class 8%) wasadded under stirring and the temperature kept at consisting ofwater-soluble polyamides derived from polyalkylene polyarnines anddicarboxylic acids and dicyandiarnide formaldehyde polycondensationproducts at a pH of from about 3.0 to about 4.0 and a temperature offrom about 60 C. to about 90 C. for a period of from about 1 minute toabout 10 minutes, said cationizing agent being employed in an amount offrom about 1 to about 50 Weight percent based on the weight of thedialdehyde polysacch'aride and adding the resulting cationizeddialdehyde polysaccharide to an aqueous slurry of cellulosic fibers.

2. A process according to claim 1 wherein the cationizing agent is awater-soluble polyamide derived from polyalkylene polyarnines anddicarboxylic acids.

3. A process according to claim 1 wherein the cationizing agent is adicyandiamine-formaldehyde polycondensation product.

4. A process according to claim 1 wherein the dialdehyde polysaccharideis dialdehyde starch.

References Cited by the Examiner UNITED STATES PATENTS 2,302,310 11/1942Glarum et al. 106213 2,566,842 9/1951 Landes et a1. 106213 3,016,325 1/1962 Pattilloch 162182 3,067,088 12/1962 Hofreiter et a1. 1621753,100,203 8/1963 Borchert 260209 3,138,473 6/1964 Floyd et al 106--163ALEXANDER H. BRODMERKEL, Primary Examiner.

ALFRED L. LEAV'IT I, Examiner.

L. HAYES, Assistant Examiner.

1. A PROCESS FOR IMPROVING THE PHYSICAL PROPERITES OF CELLULOSICMATERIALS WHICH COMPRISES REACTING AN AQUEOUS DISPERSION OF A DIALDEHYDEPOLYSACCHARIDE CONTAINING FROM ABOUT 1 TO ABOUT 30% WEIGHT PERCENT OFTHE DIALDEHYDE POLYSACCHARIDE WITH A WATER-SOLUBLE POLYMERICNITROGEN-CONTAINING CATIONIZING AGENT SELECTED FROM THE CLASS CONSISTINGOF WATER-SOLUBLE POLYAMIDES DERIVED FROM POLYALKYLENE POLYAMINES ANDDICARBOXYLIC ACIDS AND DICYANDIAMIDEFORMALDEHYDE POLYCONDENSATIONPRODUCTS AT A PH OF FROM ABOUT 3.0 TO ABOUT 4.0 AND A TEMPERATURE OFFROM ABOUT 60* C. TO ABOUT 90* C. FOR A PERIOD OF FROM ABOUT 1 MINUTE TOABOUT 10 MINUTES, SAID CATIONIZING AGENT BEING EMPLOYED IN AN AMOUNT OFFROM ABOUT 1 TO ABOUT 50 WEIGHT PERCENT BASED ON THE WEIGHT OF THEDIALDEHYDE POLYSACCHARIDE AND ADDING THE RESULTING CATIONIZED DIALDEHYDEPOLYSACCHARIDE TO AN AQUEOUS SLURRY OF CELLULOSIC FIBERS.